Miniaturized gas refrigeration device with two or more thermal regenerator sections

ABSTRACT

The size of a miniature cryocooler operating on the Stirling refrigeration cycle is further reduced by shortening a first thermal regenerator module (R) disposed on a cold side of a thermal barrier (T) and providing a second thermal regenerator module (R 1 ) disposed on a warm side of the thermal barrier (T). A thermally insulated fluid flow passage is disposed to interconnect the first and second regenerator modules to thermally insulate the fluid passage. In combination, the first and second regenerator modules provide 100% thermal regenerator effectiveness in the device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/433,376 filed May 12, 2006 and entitled “MINIATURIZED GASREFRIGERATION DEVICE WITH TWO Oreg. MORE THERMAL REGENERATOR SECTIONS,”which is hereby incorporated by reference in its entirety.

This application is related to U.S. patent application Ser. No.11/432,957 filed May 12, 2006 and entitled “CABLE DRIVE MECHANISM FORSELF-TUNING REFRIGERATION GAS EXPANDER” (now U.S. Pat. No. 7,555,908),U.S. patent application Ser. No. 11/433,697 filed May 12, 2006 andentitled “COOLED INFRARED SENSOR ASSEMBLY WITH COMPACT CONFIGURATION”(now U.S. Pat. No. 7,587,896), and U.S. patent application Ser. No.11/433,689 filed May 12, 2006 and entitled “FOLDED CRYOCOOLER DESIGN”(now U.S. Pat. No. 8,074,457), which are hereby incorporated byreference in their entirety.

BACKGROUND

1. Field of the Invention

The invention provides an improved refrigeration device. In particular,the improved refrigeration device includes one or more thermalregenerator for exchanging thermal energy with a refrigeration gas withat least one of the thermal regenerator disposed distal from the coldend of the device.

2. Description of Related Art

A cryogenic refrigeration device includes a sealed working volume filledwith a working refrigeration fluid, e.g. comprising helium gas. Such adevice may be used to cool an element to temperatures below 100.degree.K (degrees Kelvin). An example refrigeration device 10 of the prior artis shown in section view in FIG. 1. The device 10 is a miniaturizedrefrigeration device includes a gas compression unit 12 and a volumecontrol unit 14. The compression unit 12 and volume control unit 14 areinterconnected by a first fluid conduit 16. The sealed working volume ofthe example device at least includes the internal volumes of thecompressor unit 12, the fluid conduit 16 and the volume control unit 14.Miniature cryogenic refrigeration devices are commercially availablethat are configured with the gas compression unit, the volume controlunit, and the fluid conduit all integrally formed in a unitary assemblysuch as a crankcase. Examples of these devices are disclosed in U.S.Pat. No. 3,742,719 by Lagodmos, in U.S. Pat. Nos. 5,197,295 and4,514,987 by Pundak et al, in U.S. Pat. No. 6,327,862 by Hanes, and inU.S. Pat. No. 4,858,442 by Stetson.

Other miniature cryogenic refrigeration devices are commerciallyavailable that are configured with the gas compression unit separatefrom the volume control unit, and with the fluid conduit extendedbetween the separated units. Examples of these devices are disclosed inU.S. Pat. Nos. 5,596,875 and 4,024,727 by Berry et al., in U.S. Pat. No.4,711,650 by Farie et al. and in U.S. Pat. No. 6,397,605 by Pundak.

In FIG. 1, the conventional gas compression unit 12 comprises acompression cylinder bore 18 formed within a surrounding crankcase 20and a cylindrical compression piston 22 movably disposed within thecompression cylinder bore 18 and movable in response to a driving forceapplied to the compression piston 22 by a drive link 24. A cylinder head26 attaches to the crankcase 20 to seal a compression end of thecylinder bore 18. A cylindrical compression volume 28 is formed at thecompression end of the cylinder bore 18 between the piston 22 and thecylinder head 26. Reciprocal movement of the piston 22 along alongitudinal axis of the cylinder bore 18 cyclically varies the volumeof the compression volume 28, and consequentially cyclically varies thevolume of the entire working volume. Accordingly, movement of the piston22 generates a pressure wave that propagates through the working volume.The pressure wave is generated in the compression volume 28 andpropagates through the first fluid conduit 16 to the volume control unit14 and through the volume control unit 14 to a sealed end thereof. Thepressure pulse is reflected by the sealed end and propagates backtowards the compression volume 28. Accordingly, the refrigeration gasflows bi-directionally through the working volume with peak pressureamplitudes occurring as the piston 22 is driven toward the cylinder head26 and with minimum pressure amplitudes occurring as the piston 22 isdrawn away from the cylinder head 26.

The volume control unit 14 comprises a cylinder housing 30 formed tosurround a longitudinal bore or cylinder 32. The cylinder 32 is open atone end to receive a gas displacing piston 36 therein and is sealed at aclosed end by an end cap 34. The gas displacing piston 36 is movablewithin the cylinder 32 and is reciprocally driven along the cylinderlongitudinal axis by a drive link 38. Movement of the gas displacingpiston 36 cyclically varies the volume of a gas expansion space 40formed between the inner most end of the gas displacing piston 36 andthe end cap 34. Each cycle of the refrigeration device 10 coolsrefrigeration gas contained within the expansion space 40. An element tobe cooled 42 attaches to the end cap 34 and cooled by the refrigerationgas inside the expansion space 40. A fluid port 44 provides fluidcommunication between the first fluid conduit 16 and the cylinder 32.

A fluid control module, generally designated F, receives high pressurerefrigeration fluid from the compression unit 12 through the port 44.Elements of the cylinder housing 30 and the gas displacing piston 36combine to provide a clearance seal at the open end of the cylinder 32,which prevents refrigeration gas from escaping from the cylinder 32while still allowing movement of the gas displacing piston 36. The gasdisplacing piston 36 is configured with internal fluid passages 46extending from the port 44 to a regenerator R, described below.

A regenerator module R comprises an insulating regenerator tube 48formed as a fluid conduit and filled with a regenerator matrix 50comprising a porous solid material configured to exchange thermal energywith the refrigeration gas as the gas flows through the regenerator tube48. The regenerator module R receives incoming warm refrigeration gas athigh pressure from the fluid control module F. The refrigeration gasflows through the regenerator tube 48 and exchanges thermal energy withthe regenerator matrix 50 before flowing into the expansion space 40. Ona return path, cold low pressure refrigeration gas exiting from theexpansion space 40 flows through the regenerator module R, cooling theregenerator matrix 50 before flowing back to the compression unit 12.

A thermal barrier T, designated schematically by the dashed line in FIG.1, comprises one or more thermally insulating elements disposed toprevent thermal conduction across the thermal barrier T. Generallyelements on the warm side of the thermal barrier T are at the localambient temperature, or a higher temperature due to heat dissipation inthe compression unit 12 and drive motors, not shown, and elements on thecold side of the thermal barrier T are below the ambient temperature.During operation, the expansion space 40, also called a cold tip or coldend, is maintained at a cryogenic temperature, e.g. 77.degree. K, whilethe fluid control module F and the compression unit 12 remainsubstantially at the local ambient temperature, e.g. 270.degree. K.Accordingly, a very steep thermal gradient extends along thelongitudinal length of the regenerator module R.

It is well understood that using a regenerator module R to pre-coolrefrigeration gas or another working fluid as it flows from thecompression unit 12 to the expansion space 40 increases the coolingpower that can be delivered to the element to be cooled 42. In addition,pre-heating refrigeration gas as it flows from the expansion space tothe compressor improves the efficiency of the refrigeration device.Ideally a regenerator module R is designed for 100% effectiveness whichmeans that the regenerator module completely pre-cools, or pre-heats,the refrigeration gas flowing along its length. In particular, 100%effectiveness occurs when warm refrigeration gas entering theregenerator module at the warm end exits the regenerator module at thecold end at the cooling temperature of the device, e.g. 77.degree. K.When this is the case, substantially all of the cooling power generatedby expanding the expansion space 40 volume is available to be deliveredto the device to be cooled 42 and none of the cooling power generated bythe device is needed to further cool the entering refrigeration gas.Conversely, 100% effectiveness occurs when cold refrigeration gasentering the regenerator module at the cold end exits the regeneratormodule at the warm end at the local ambient temperature, e.g.270.degree. K. When this is the case, substantially all of the coolingavailable from the cold refrigeration gas is transferred to theregenerator matrix 50. Analytical models have shown that any reductionin the effectiveness of the regenerator greatly degrades the coolingpower of the refrigeration device. In one example, Applicants calculatedthat a conventional refrigeration device of the type shown in FIG. 1 maybe reduced to 80% of its potential cooling power when the regeneratormatrix is 99% effective instead of 100% effective.

It is further understood that the effectiveness of a regenerator is afunction of the magnitude of the total surface area of surfaces of theregenerator matrix substrate that contact working fluid and further thatthe total surface area is strongly dependent upon the longitudinallength L of the regenerator module R. Heretofore it has been a harddesign requirement of a miniature cryocooler refrigeration system thatthe regenerator matrix 50 be configured with sufficient longitudinallength L for making a 100% effective thermal energy exchange with therefrigeration gas flowing along its length. However this hard designrequirement is in conflict with reducing the size of the refrigerationdevice 10.

Generally there is a need in the art to further miniaturizerefrigeration devices or at least to further miniaturize the volumecontrol unit 14 to deliver cooling power to smaller elements to becooled 42 or to fit the refrigeration device 10 or the volume controlunit 14 within smaller volume enclosures. A major barrier to reducingthe size of the refrigeration device 10 or the size of the volumecontrol unit 14 has been an inability to reduce the longitudinal lengthL of the regenerator matrix 50 while still providing a 100% thermalenergy exchange with the working fluid.

Heretofore, miniature refrigeration devices like the one shown in FIG. 1have employed a single regenerator matrix 50 disposed in the regeneratormodule R and more specifically with the entire longitudinal length L ofthe regenerator module disposed on the cold side of the thermal barrierT. Such a system configuration is not easily miniaturized. According tothe present invention, the overall size of a refrigeration device isreduced by configuring the device with a longitudinal length L of aregenerator matrix disposed on the cold side of the thermal barrier to alength L that is less than a length L required for 100% effectivenessand other regenerator modules are disposed on the warm side of thethermal barrier T to add further regenerating capacity as may berequired to provide 100% regenerator effectiveness.

BRIEF SUMMARY

The present invention overcomes the problems cited in the prior art byproviding a refrigeration device configured with a first regeneratormodule disposed on a cold side of a thermal barrier and a secondregenerator module disposed on a warm side of the thermal barrier and athermally insulated fluid flow passage disposed to interconnect thefirst and second regenerators.

In one example a first regenerator module (R) is disposed in aregenerator portion of a movable gas displacing piston (138) and asecond regenerator module (R₁) is disposed in a fluid control unit (152)of the movable gas displacing element (138). Cold refrigeration gasenters the first regenerator module (R) from an expansion space (142)and cools a thermal regenerator substrate contained therein. However,the first regenerator module does not provide a 100% thermal energyexchange with the refrigeration gas.

A thermal barrier (T) is disposed between the first regenerator module(R) and the second regenerator module (R₁). The thermal barrier Tincludes insulating elements disposed to create a high resistance tothermal energy conduction between the first regenerator module (R) andthe second regenerator module (R₁). Refrigeration gas exiting the firstregenerator module is below the local ambient temperature so a fluidconduit connecting the first regenerator module and the secondregenerator module is insulated to prevent the refrigeration gas flowingtherein to become warmed by surrounding elements. In addition the secondregenerator module R₁ is also insulated to prevent the refrigeration gasflowing there through and to prevent the regenerator matrix materialcontained therein from being warmed by surrounding elements. The secondregenerator module R₁ completes the thermal energy exchange with therefrigeration gas as it flows through such that refrigeration gas exitsthe second regenerator module R₁ at the local ambient temperature. Thefirst and second regenerator modules combine to complete a 100%effective thermal energy exchange with the refrigeration gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention will best be understood from adetailed description of the invention and a preferred embodiment thereofselected for the purposes of illustration and shown in the accompanyingdrawing in which:

FIG. 1 illustrates a section view taken through portions of conventionalrefrigeration device.

FIG. 2 illustrates a section view taken through portions of an improvedrefrigeration device utilizing two regenerator modules according apreferred embodiment of the present invention.

FIG. 3 illustrates a section view taken through an improved gasdisplacing piston utilizing two regenerator modules according to apreferred embodiment of the present invention.

FIG. 4 illustrates a section view taken through portions of an improvedrefrigeration device utilizing two regenerator modules according to asecond embodiment of the present invention.

FIG. 5 illustrates a section view taken through portions of an improvedrefrigeration device utilizing three regenerator modules according to athird embodiment of the present invention.

FIG. 6A illustrates a preferred regenerator element shown in side view.

FIG. 6B illustrates a preferred regenerator element shown in top view.

FIG. 7 illustrates an external view of a miniature refrigeration deviceconfigured according to the present invention.

DETAILED DESCRIPTION

FIG. 2 depicts a section view taken through portions of a preferredembodiment of an improved refrigeration device 100 according to thepresent invention. The device 100 includes a sealed working volumefilled with a working refrigeration fluid such as helium gas; however,other working fluids are usable. In particular, the refrigeration device100 includes a gas compression unit 110 and a gas volume expansion unit112. The compression unit 110 and volume expansion unit 112 are fluidlyinterconnected by a first fluid conduit 114, and the combined internalvolume of these elements forms the working volume. The device 100 isconstructed to establish a thermal barrier T which substantially blocksthermal conduction from crossing the dashed line shown in FIG. 2 todemark an approximate boundary between a warm side of the device shownon the left in FIG. 2 and a cold side of the device, shown on the rightin FIG. 2. During operation, elements on the warm side of the thermalbarrier T substantially remain at the local ambient temperature whileelements on the cold side of the thermal barrier T are cooled totemperatures that are substantially below the local ambient temperature.However, according to a first embodiment of the present invention, shownin FIG. 2 and described below, a first regenerator module R is disposedon the cold side of the thermal barrier T and a second regeneratormodule R₁ is disposed on the warm side of the thermal barrier T. Infurther embodiments of the present invention, shown in FIGS. 4 and 5, afirst regenerator module R is disposed on the cold side of the thermalbarrier T and a third regenerator module R₂ is disposed on the warm sideof the thermal barrier T.

As shown in FIG. 2, the gas compression unit 112 comprises aconventional gas compressor formed with a compression cylinder 116 boredin a crankcase support 118 and sealed by a cylinder head 120. Acompression piston comprises a disk shaped piston head 124 and anannular piston side wall 126. An outside diameter of the piston sidewall 126 is sized to fit within the compression cylinder 116 with a gassealing clearance fit. The gas sealing clearance fit comprises anannular gap, not shown, between the compression cylinder 116 and theside wall 126 and the annular gap dimension is sized to substantiallyprevent pressurized refrigeration gas from escaping from the compressioncylinder 116 while still providing sufficient clearance to allowmovement of the piston 122 with respect to the cylinder 116. Inparticular, the annular gap dimension may be in the range of0.001-0.0015 mm, (50-100 micro inches) and the gap dimension may beformed even smaller when practical forming techniques allow it.

A cylindrical gas compression volume 128 is formed in the compressioncylinder 116 between the piston head 124 and the cylinder head 120. Thepiston 122 is reciprocally moved within the compression cylinder 116 tocyclically vary the volume of the gas compression volume 128. The pistonmovement generates a pressure pulse within the working volume and thepressure pulse reaches maximum pressure amplitude as the piston isadvancing toward the cylinder head 120. Conversely, the pressure pulsereaches minimum pressure amplitude when the piston is being drawn awayfrom the cylinder head 120.

The pressure pulse propels refrigeration gas out of the compression unit110, through the first fluid conduit 114 and into the volume expansionunit 112. The pressure pulse may also reflect from a sealed end of thevolume expansion unit 112 causing refrigeration gas to flow back towardthe compression unit 112 during the low amplitude phase of the pressurepulse. In other embodiments of the refrigeration device 100, such as aVuilleumier refrigerator, a heating element 130 may be mounted proximateto the compression volume 128 to further increase the pressure of theworking fluid by heating it.

Volume Expansion Unit

The gas volume expansion unit 112 generally comprises a fluid controlmodule F, shown on the left in FIG. 2, a first regenerator module R, asecond regenerator module R₁, housed within the fluid control module F,and a volume expansion module V, shown on the right in FIG. 2. The fluidcontrol module F is in fluid communication with the first fluid conduit114 and with the first regenerator module R such that working fluidflows bi-directionally through the fluid control module F and throughthe second regenerator module R₁ housed therein. The fluid controlmodule F also seals an open end of the volume expansion unit 110 toprevent pressurized refrigeration gas from escaping from the expansionunit 112.

The first regenerator module R is in fluid communication with the fluidcontrol module F and the expansion module V such that working fluidflows bi-directionally through the first regenerator module R. Each ofthe first and second regenerator modules comprise a fluid conduit filledwith a porous solid regenerator matrix such that working fluid flowingthrough the regenerator modules flows through the regenerator matrices.As the working fluid flows through each regenerator matrix thermalenergy is exchanged between the working fluid and the correspondingregenerator matrix.

The volume expansion module V receives working fluid from the firstregenerator module R. The volume of the volume expansion module V isconfigured to be expandable, substantially in phase with peaks inpressure pulse amplitude of the working fluid, to generate cooling powerby a refrigeration effect that occurs by expanding the volume of thepressurized refrigeration gas. An element to be cooled 146 is positionedproximate to the volume expansion module V and is cooled by the coolingpower generated therein. When the volume expansion module V iscollapsed, the refrigeration gas is forced to flow out of the volumeexpansion module V and back towards the compression unit 110 through thefirst regenerator module R.

The volume expansion unit 112 comprises a cylinder housing 132 formedwith contiguous annular wall sections enclosing a cylindrical volume orvolume expansion cylinder 134. The cylinder 134 extends along the entirelongitudinal length of the cylinder housing 132 and is open at a warmend thereof, shown on the left side of FIG. 2, and closed and pressuresealed by an end cap 136, attached to the annular wall sections at acold end thereof, shown on the right of FIG. 2.

The volume expansion unit 112 further comprises a gas displacing pistongenerally indicated by the reference numeral 138, and shown in detail inFIG. 3. The gas displacing piston 138 installs into the cylinder 134through the open warm end and is movable with respect to the cylinderhousing 132 along a longitudinal axis 140 of the cylinder 134. The gasdisplacing piston 138 includes a cold end 139 installed innermost in thecylinder 134 and a warm end 141 being driven by a drive link 144. Thegas displacing piston 138 has a longitudinal length that is sized tofill the cylinder 134 except for a hollow volume at the cold end of thecylinder 134. The hollow volume comprises the volume expansion module Vdefined by a variable volume gas expansion space 142 that extends fromthe cold end 139 to the end cap 136.

The volume of the gas expansion space 142 varies as the gas displacingpiston 138 is reciprocally moved over a stroke distance by a drive link144. A drive element, not shown, couples with the drive link 144 to movethe gas displacing piston 138 in accordance with a desired pattern. Thepattern of movement is synchronized, although phase separated, withmovement of the motion of the gas compression piston 122 for generatingrefrigeration cooling within the expansion space 142. An element to becooled 146 is attached to the end cap 136 and thermal energy may beremoved from the element to be cooled 146 during each cooling cycle ofthe refrigeration device.

Cylinder Housing

The cylinder housing 132 comprises a pressure vessel for containingpressurized refrigeration fluid formed by a first tube element 148, asecond tube element 160 and the end cap 136. The first tube element 148comprises a thick annular wall with a longitudinal bore passing alongits length for forming a portion of the cylinder 134 and for forming theouter housing of the fluid control module F. The first tube element 148is supported by a support structure 150 which may be unitary with thegas compression unit crankcase 118. Alternately, the first tube element148 may comprise a cylinder bore formed directly in the crankcase 118.In other configurations, the support structure 150 may comprise aseparate support element, e.g. when the volume expansion unit 112 andthe gas compression unit 110 are formed as separate elements (split)connected by the fluid conduit 114.

The second tube element 160 comprises a thin-walled expansion tubehaving a warm end attached to the first tube element 148 and a cold endcantilevered from the first tube element 148. The second tube element160 is cantilevered from the first tube element 148 and supportstructure 150 to thermally isolate the cold end from warm element. Adisk-shaped end cap 136 is joined to second tube element 160 at its coldend. The first tube element 148, the second tube element 160 and the endcap 136 are each formed from metal e.g. stainless steel, to provide theneeded strength and stiffness for forming the cylinder housing 132 whichis a pressure vessel. In a preferred embodiment the first and secondtubes 148 and 160 are joined together by a continuous laser weld and theend cap 134 is joined to the second tube by a continuous laser weld toensure that the cylinder 134 is pressure sealed. However, other pressuresealing joining techniques are usable.

The entire length of the second regenerator tube 160 extends to the coldside of the thermal barrier T which as shown in FIG. 2 is substantiallylocated at the joint between the first and second tube elements.Accordingly, the second tube element 160 is specifically configured witha thin wall, e.g. less than 0.0004 mm, (0.010 inches) to provide a highresistance to the conduction of thermal energy along the longitudinaldirection defined by 140. However, the thin wall readily conductsthermal energy in the radial direction. The element to be cooled 146 isattached to the end cap 136 and the end cap 136 is configured to conductthermal energy away from the device to be cooled 146 and toward coldrefrigeration gas contained within the expansion space 142.

Gas Displacing Piston

The gas displacing piston 138, shown in section view in FIG. 3,comprises a fluid control element 152 disposed at the warm end 141 andthe fluid control element 152 cooperates with the first tube element 148to seal the cylinder 134 and to support the gas displacing piston 138for movement within respect to the cylinder 134. The fluid controlelement 152 includes spaced apart annular bearing surfaces 154 disposedon opposite sides of a fluid port 156, and the annular bearing surfaces154 are form fitted to match the diameter of the cylinder 134 to providea gas clearance seal. The gas clearance seal prevents pressurizedrefrigeration gas from escaping from the cylinder 134 while stillallowing movement of the gas displacing piston 138 along thelongitudinal axis 140. The radial clearance of the gas clearance sealmay be in the range of 0.001-0.0015 mm, (50-100 micro inches), or less,if it can be achieved by a practical process.

The fluid control element 152 further includes a blind bore extendingfrom and sized to receive the second regenerator 182 therein. Aconnecting passage 158, shown in FIG. 2, extends from a radial surfaceof the fluid control element 152 to the blind bore and provides a fluidpassage from the blind bore to the port 156. Accordingly, refrigerationgas entering the port 156 from the first fluid conduit 114 flows intothe connecting passage 158, into the blind bore through the secondregenerator module 182 (R₁ in FIG. 2) and exits to the first regeneratormodule R.

First Regenerator Module

The first regenerator module R is integral with the gas displacingpiston 138 and comprises an insulating regenerator tube 162 which formsa fluid passage that extends from the fluid control module F to theexpansion space 142. The fluid passage is filled with a porous solidregenerator matrix material 164 configured to exchange thermal energywith the working fluid as it flows through the insulating tube. Anoutside diameter of the regenerator tube 162 is sized to provide aslight clearance fit with respect to the cylinder 134; however the coldend of the tube 162 may include a raised bearings surface 166 forbearing against the wall of the cylinder 134 during movement withrespect thereto.

As shown in FIG. 3, a warm end of the regenerator tube 162 attaches tothe fluid control unit 152 by fitting over a land diameter 165 of thefluid control unit 152. The regenerator tube 162 is formed from athermally insulating material such as an epoxy resin filled with glassfibers, e.g. G10, FR4 or Ryton. Such materials provide a high resistanceto thermal conduction in both the radial and longitudinal directions.Accordingly, thermal conduction across the contacting surfaces of thefluid control unit 152 and the regenerator tube 162 is substantiallyminimized. In a preferred embodiment, Ryton is used which comprises 40%fiberglass reinforced Poly-Phenylene Sulfide.

The regenerator tube 162 is filled with a regenerator matrix 164. In apreferred embodiment, the regenerator matrix 164 comprises a pluralityof disk-shaped elements formed from interwoven metallic wire. An exampledisk-shaped element 167 is shown in FIGS. 6A and 6B. Each disk shapedelement comprises a plurality of metallic wire strands woven togetherwith a weave pattern such as a plain or a twill weave pattern. In apreferred embodiment, the wire strands have a diameter in the range of0.012-0.050 mm, (0.0005-0.002 inches) and the wires are interwoven witha pitch of approximately 16 wires per mm, (400 wires per inch), i.e.with a center-to-center wire separation of approximately 0.064 mm,(0.0025 inches). The preferred wire material is round stainless steelwire. The regenerator matrix 164 is formed by stacking disk elements oneabove another to fill the regenerator tube 162 along its entirelongitudinal length. Depending on the longitudinal length of theregenerator tube 162, the thickness of each disk and the pressure forceapplied to compact and hold the disks within the regenerator tube 162,the regenerator matrix 164 may comprise between 600 and 1000 disk-shapedelements. In a preferred embodiment the diameter of each disk isapproximately 4.8 mm, (0.188 inches) however larger or small diameterregenerator matrix configurations are usable without deviating from thepresent invention. While any regenerator matrix material may be usablewith the present invention, specific examples of thermal regeneratormatrix configurations usable with the present invention are disclosed indisclosed in U.S. patent application Ser. No. 10/444,194 filed on May23, 2003 and entitled “LOW COST HIGH PERFORMANCE LAMINATE MATRIX”(published as US2004/0231340), the entirety of which is herebyincorporated herein by reference.

The regenerator tube 162 includes and end cap 168 attached thereto atthe cold end to hold the regenerator matrix material inside theregenerator tube 162. The end cap 168 is made with features used toattach it to the tube 162 and is provided to hold the regeneratormaterial inside the regenerator tube 162. The end cap 168 is porous toprovide fluid passages from the regenerator matrix 164 to the expansionspace 142 and the porosity of the fluid passages may be configured tocontrol flow of working fluid into and out of the regenerator matrix164. In addition, the raised bearing surface 166 may be formed on theend cap 168 instead of on the end of the regenerator tube element 160.

One or more thermally insulating disks 170 are installed within theregenerator tube 162 to capture the regenerator matrix elements in placeat the warm end and to provide a high resistance to thermal conductionbetween the regenerator matrix 164 and elements of the fluid controlmodule F or elements or the second regenerator module R₁. Eachinsulating disk 170 includes a flow aperture 172 passing through itscenter and through which working fluid flows into and out of theregenerator matrix 164. The insulating disks may be formed from Ryton oranother thermally insulating material.

Second Regenerator

The second thermal regenerator module R₁ is disposed within the fluidcontrol unit 152 which is on the warm side of the thermal barrier T.However, according to the present invention, an additional thermalbarrier is formed to surround the second regenerator module R₁. Thesecond regenerator module R₁ is generally constructed like the firstregenerator module R and includes a thermally insulating hollow exteriorshell portion that forms a fluid conduit along it longitudinal lengthand provides fluid flow apertures at each end thereof. The exteriorshell portion is formed from a thermally insulating material such as anepoxy resin filled with glass fibers, e.g. G10, FR4 or Ryton, with Rytonbeing the preferred enclosure material. The shell portion is filled witha second regenerator matrix 182 configured to exchange thermal energywith the working fluid as it flows through it.

As shown in section in FIG. 3, the shell portion comprises a unitary hatshaped enclosure element comprising a surrounding annular side wall 184formed to surround a hollow cylindrical cavity along its longitudinallength and a top wall 188. The cavity is opened at its bottom end andthe top wall 188 includes a fluid flow aperture 190 passing through it.A base of the annular wall 184 is terminated by an annular shoulder 192extending radially outward from the annular wall 184. The annularshoulder 192 provides an insulating seat for contacting a bottom edge ofthe fluid control element 152 and for providing a high resistance tothermal conduction between elements of the fluid control module F andthe regenerator module R.

The second thermal regenerator module R₁ is filled with a regeneratormatrix substrate 182 which may comprise any regenerator matrix but whichpreferably formed by a plurality of disk-shaped element like the element167 shown in FIGS. 6A and 6B. Each disk-shaped element 167 of the secondregenerator matrix 182 is formed with a diameter that closely matchesthe inside diameter of the annular wall 184 and the disks 167 arestacked one above another to entirely fill the cavity 186. As describedabove, each disk-shaped elements 167 may be formed from plurality ofmetallic strands of stainless steel wire with a diameter in the range of0.012-0.050 mm, (0.0005-0.002 inches) woven together with a plane ortwill weave pattern a pitch of approximately 16 wires per mm, (400 wiresper inch), i.e. with a center-to-center wire separation of approximately0.064 mm, (0.0025 inches). Depending on the cavity longitudinal length,the thickness of each disk and the pressure force used to compact thedisks within the annular wall 180, the second regenerator matrix 186 maycomprise between 50-200 disk-shaped elements.

In a preferred embodiment of the present invention the diameter of eachdisk of the second regenerator matrix 182 has an approximate diameter of2.54 mm, (0.1 inches); however larger or small diameter regeneratormatrix configurations are usable without deviating from the presentinvention. In addition, the disk-shaped elements of the secondregenerator matrix 182 may be installed into the cavity 186 with theweave pattern of each disk being randomly oriented, or with the weavepattern of alternating disks being aligned with a desired orientation.

Drive Motor

In a preferred embodiment of the present invention a single rotary drivemotor, not shown, is coupled to the compression unit drive link 130 andto the gas displacing piston drive link 152. With each full revolutionof the drive motor each of the compression piston 122 and gas displacingpiston 138 traverses a round trip reciprocal motion over its designedstoke distance. The reciprocal motion of the compression piston 122alternately expands and contracts the volume of the compression volume126 to generate gas pressure pulses while the reciprocal motion of thegas displacing piston 138 alternately expands and contracts the volumeor the expansion space 142 to generate a refrigeration effect.Generally, the motion of the two pistons is phased to position thecompression piston 122 at its maximum compression stroke (i.e. tominimize the compression space volume) just as the gas displacing piston138 begins moving to expand the volume of the expansion space 142.Generally, the preferred refrigeration device 100 operates as Stirlingrefrigeration device such as the one disclosed in commonly assigned U.S.Pat. No. 4,858,442 by Stetson, the entire content of which is herebyincorporated herein by reference. An example rotary DC motor andcoupling a coupling device usable with the present invention isdisclosed in co-pending and commonly assigned U.S. patent applicationSer. No. 10/830,630, by Bin Nun et al., filed on Apr. 23, 2004, entitledREFRIGERATION DEVICE WITH IMPROVED DC MOTOR, the entire content of whichis hereby incorporated herein by reference.

Accordingly, working fluid, e.g. a refrigeration gas comprising helium,at high pressure is forced from the gas compression volume 128 to thesecond regenerator R₁ which starts to pre-cool the gas. Thereafter therefrigeration gas enters the first regenerator module R which furtherpre-cools the refrigeration gas which then flows into the expansionspace 142, which is at a minimum volume condition. When the expansionspace 142 is filled with high pressure refrigeration gas the gasdisplacing piston 138 is moved to increase the volume of the expansionspace 142 and the refrigeration gas contained therein is cooled. As thegas displacing piston 138 is moved to decrease the volume of theexpansion space 142, the cold refrigeration gas is expelled from theexpansion space 142 and flows through the first regenerator module R andthe cold refrigeration gas cools the regenerator matrix 164. Therefrigeration gas next flows through the second regenerator module R₁and cools the regenerator matrix 182.

Energy Exchange

As stated above, a thermal regenerator matrix is considered 100%effective when a volume of cold refrigeration gas enters the regeneratormatrix at a cold temperature of the device and exits the regeneratormatrix a warm temperature of the device. Conversely, a thermalregenerator matrix is considered 100% effective when a volume of warmrefrigeration gas enters the regenerator matrix at a warm temperature ofthe device and exits the regenerator matrix a cold temperature of thedevice. In the refrigeration device 100, the cold temperature of thedevice is approximately 77.degree. K, which is the temperature of therefrigeration gas contained within the expansion space 142, and the warmtemperature is substantially the local ambient temperature, e.g.270.degree. K. Of course the local ambient temperature may varyaccording to the location and application of the device 100 and the warmtemperature of the device may be slightly elevated with respect to thelocal ambient temperature due to thermal dissipation of electrical andmechanical elements of the device 100 and the actual warm temperaturemay be in the approximate range of 220.degree.-320.degree. K.

According to the invention, the device 100 includes two distinct andseparate regenerator modules R and R₁ and each regenerator R and R₁ hasa regenerator effectiveness capacity that is less than 100%. However,the combined regenerator effectiveness capacity of the two regeneratormatrices 164 and 182 provides a 100% effective thermal energy exchangewith the refrigeration gas flowing through the device 100. Specifically,the first regenerator module R includes a regenerator matrix 164 that isconfigured with a longitudinal length L that is less than a length Lthat is required to provide a 100% effective thermal energy exchange bythe matrix 164. The length L of the regenerator matrix 164 isspecifically shortened to further miniaturize the refrigeration device100 by shortening the length of the volume expansion unit 112.Accordingly, the first regenerator module R is less than 100% effectiveby design.

To add additional regenerator capacity to the device 100, the secondregenerator module R₁ is provided in the flow path of the refrigerationgas, between the gas expansion space 142 and the gas compression volume128. The second regenerator module R₁ is disposed inside the fluidcontrol unit 152 which allows the addition of regenerator effectivenesscapacity without increasing the volume of the device 100 or the lengthof the volume expansion unit 112. However, the second regenerator moduleR₁ is located on the warm side of the thermal barrier T and is thereforesurrounded by ambient temperature elements at approximately220.degree.-320.degree. K. Accordingly, the second regenerator module R₁is enclosed with a thermally insulating enclosure to thermally isolatethe regenerator matrix 182 and the refrigeration gas flowingtherethrough and to block thermal conduction to the second regeneratormatrix 182.

The combined thermal regenerator effectiveness of the first regeneratormodule R and the second regenerator module R₁ provides a 100% effectivethermal energy exchange with the refrigeration gas. In particular, thedevice 100 is configured such that the refrigeration gas at atemperature of approximately 77.degree. K enters the regenerator matrix164 and flows along it length L. The gas exits the regenerator matrix164 at a temperature that is below the local ambient temperature. Thegas then enters the second regenerator matrix 182 and flows along itslength and exits the regenerator matrix 182 substantially at the sametemperature as the local ambient temperature, e.g. approximately270.degree. K. In this case, both regenerator matrices 164 and 182 arecooled by the refrigeration gas flowing from the expansion space 142 tothe compression volume 128 and both regenerator matrices 164 and 182pre-cool the refrigeration gas as it flows from the compression volume128 to the expansion space 142.

The effectiveness of a thermal regenerator matrix is strongly dependentupon the total surface area of matrix elements making contact with therefrigeration gas as it flows through the matrix, by the flow velocityof the gas flowing through the matrix, and by the thermal energyexchange characteristics of the matrix substrate. With other parametersremaining constant, the longitudinal flow length of a regenerator matrixis directly proportional to is regenerator effectiveness. In the device100, the second regenerator matrix 182 is configured to provide aregenerator effectiveness capacity that is equal to a length ΔL of theregenerator matrix 164. Accordingly, the addition of the secondregenerator matrix 182 allows the first regenerator matrix 164 to beshortened by a length ΔL without a reduction in regenerator matrixeffectiveness of the system.

In the particular example of a preferred embodiment of the presentinvention, the first regenerator matrix 164 has a longitudinal length of34.45 mm, (1.36 inches) and comprises approximately 600-1000 disk-shapedelements each having a diameter of 4.8 mm, (0.19 inches). The secondregenerator matrix 186 has a longitudinal length of approximately 12.7mm, (0.5 inches) and comprises approximately 50-500 disk-shaped elementseach having a diameter of 2.54 mm, (0.1 inches). The regeneratoreffectiveness of the second regenerator matrix 186 is equivalent to theregenerator effectiveness of a length.DELTA.L of the first regeneratormatrix 164 and the length.DELTA.L is equal to approximately 4.7 mm,(0.183 inches). Accordingly, the length of the volume expansion unit 112of the improved refrigeration device 100 of the present invention isreduced by 4.7 mm, (0.183 inches) as compared to the conventionalrefrigeration device 10 of FIG. 1, which has substantially similarconstruction and performance characteristics as the device 200 bututilizing only a single regenerator module R.

Third Regenerator

In a further embodiment according to the present invention, arefrigeration device 200 is shown in FIG. 4. The refrigeration device200 is generally configured similarly to the refrigeration device 100and the same reference numbers are used to designate like elements. Thedevice 200 includes a gas compression unit 110, with a gas compressionvolume 128, a gas volume expansion unit 112, with expansion cylinderhousing 132 and cylinder 136 and with a gas expansion space 142 at itscold end, and with these elements similarly configured and operating onthe same refrigeration cycle as is described above for the device 100.

The refrigeration device 200 includes a gas displacing piston thatincludes a fluid control element 204, configured to seal the warm end ofthe cylinder 136, and a first regenerator module R that extends from thefluid control element 204 to the expansion space 142. The firstregenerator module R is identical to the first regenerator module Rdescribed above for device 100. The fluid control element 204 includesinternal passages that extend from the insulating disks 170 to a fluidport 208. The fluid port 208 passes through a thick-walled first tubeelement 148 and interfaces with a third generator module R₂. The thirdregenerator module R₂ is disposed between the gas compression unit 110and the volume expansion unit 112.

The third regenerator module R₂ comprises a thermally insulating tube212 having an annular wall surrounding a hollow cylindrical cavity. Thecavity is filled with a regenerator matrix material 216 for exchangingthermal energy with working fluid flowing through the cavity. Theregenerator matrix 216 may comprise any regenerator matrix substratematerial, but is preferably is formed by a plurality of stackeddisk-shaped elements 167, as described above, with each disk-shapedelement having a diameter formed to match an inside diameter of thecavity. At each end of the insulating tube 212 is disposed an insulatingdisk-shaped element 218. Each insulating disk-shaped element 218includes a centered flow aperture formed therethrough to allow thebi-directional flow of refrigeration gas into and out of each end of theinsulating tube 212. The insulating disks 218 substantially preventthermal conduction between the matrix 216 and surrounding elements whilealso capturing the disk-shaped elements 167 within the cavity.

The internal passages of the fluid control element 152 include a blindlongitudinal bore 220 and a radial bore 222. The radial bore 222 isformed along a radial axis of the fluid control element 204 andsubstantially aligns with the port 208. The longitudinal bore extendsfrom the insulating disks 170 to the radial bore 222 and fluidlyconnects therewith. Accordingly, refrigeration gas flowsbi-directionally from the first regenerator matrix 164 through the flowapertures or the insulating disks 170, through the longitudinal bore220, the radial bore 222, the port 208, the through the insulating disks218, through the cavity housing the third regenerator R₂ and through afluid conduit 224 to the gas compression volume 128.

The longitudinal bore 220, the radial bore 222 and the fluid port 208are each surrounded by a layer of thermally insulating material providedto substantially prevent the exchange of thermal energy betweenrefrigeration gas flowing therethrough and the fluid control element 152and the first tube element 148. The layer of thermally insulatingmaterial may comprise tube elements formed from thermally insulatingmaterial and cut to length to fit within the longitudinal bore 220, theradial bore 222 and the port 208. As shown in FIG. 4 the tubes installedin the longitudinal bore and radial bore are cut at 45 degree where theymate. Each tube may be formed an epoxy resin filled with glass fibers,e.g. G10, FR4 or Ryton. The thermally insulating tubes may be fastenedin place, e.g. by a bonded joint or by a press fit.

The third regenerator R₂ may be disposed within a cylindrical cavitybored into a support element 226. The support element 226 is preferablythe unitary crankcase 118 that supports both the compression unit 110and the volume expansion unit 112. Alternately, if the compression unit110 and volume expansion unit 112 are separated, the support element 226may be formed integral with the first tube element 148, or may beindependent of the crankcase 118 or the first tube element 148. Inanother embodiment, the third regenerator R₂ may be disposed at anyposition between the compression volume 128 and the port 208 with thefluid conduit 224 extending from each end of the third regeneratormodule R₂ to the compression volume 128 and the port 208.

Because the third regenerator module is disposed external to the gascompression unit 110 and the gas volume expansion unit 112 thecross-section and length of the third regenerator module R₂ are lessrestricted by volume constraints, especially in that case that the gascompression unit 110 and volume expansion unit 112 are separated.Accordingly, the refrigeration unit 200 may comprise a third regeneratorR₂ configured with the same or greater regenerator effectiveness as theregenerator effectiveness of the first regenerator matrix R.

As an example, the first regenerator matrix 164 and the thirdregenerator matrix 216 may comprises identical disk-shaped elements 167with each regenerator matrix being configured with elements having thesame diameter, the same orientation characteristics and the samecompacting force. In this case, the first and third regenerator matriceshave substantially identical regenerator effectiveness per unit length.In this example, the length of the first regenerator matrix 164 can bereduced by amount equal to the length of the third regenerator matrix216 in a configuration that can be used to even further reduce thelength of the gas volume expansion unit 112. Another advantage of thisexample embodiment is that only one size regenerator screen is requiredand this provides a manufacturing cost savings.

As a further example, the third regenerator matrix 216 may comprisesdisk-shaped elements 167 having a greater diameter than the disk-shapedelements 167 of the first regenerator matrix 164 such that theregenerator effectiveness per unit length of the third regeneratormatrix 216 is greater than the regenerator effectiveness per unit lengthof the first regenerator matrix 164. In this case, the length of thefirst regenerator matrix 164 can be reduced by an amount ΔL utilizing athird regenerator matrix 216 configured with a length that is less thanthe length ΔL. This embodiment is especially suited for encasing thethird regenerator R₂ inside the crankcase 118.

Generally, the cross-sectional area and length of the third regeneratormatrix 216 may be larger or smaller than the cross-sectional area andlength of the first regenerator matrix 164 and may in some applicationscompletely replace the first regenerator matrix 164 to significantlyreduce the length of the gas expansion unit 112. However, in all cases,the combined thermal regenerator effectiveness of the first regeneratormatrix 164 and the third regenerator matrix 216 provides a 100%effective thermal energy exchange with the refrigeration gas. Inparticular, the thermal regenerators of the device 200 are configured toreceive refrigeration gas from the expansion space 142, at a coldtemperature of approximately 77.degree. K, and to sufficiently warm therefrigeration gas as it flows through the first regenerator matrix 164and then through the third regenerator matrix 216, to deliver therefrigeration gas out of the third regenerator matrix 216 at a warmtemperature of approximately 270.degree. K. Of course otherrefrigeration device configuration may operate at other cold and warmtemperatures without deviating from the present invention.

Three Regenerators

In a still further embodiment according to the present invention, arefrigeration device 300 is shown in FIG. 5. The refrigeration device300 is generally configured similarly to the refrigeration devices 100and 200 described above and the same reference numbers are used todesignate like elements. The device 300 includes a gas compression unit110, with a gas compression volume 128, a gas volume expansion unit 112,with expansion cylinder housing 132 and cylinder 134, and with a gasexpansion space 142 at its cold end, and with these elements similarlyconfigured and operating on the same refrigeration cycle as is describedabove for the device 100.

As shown, the device 300 includes a first regenerator module R disposedat the cold end of a gas displacing piston 302, a second regeneratormodule R₁ disposed inside a fluid control unit 304, and a thirdregenerator module R₂ disposed between the gas compression unit 110 andthe gas volume expansion unit 112. A fluid conduit 306 interconnects thethird regenerator module R₂ and the gas compression volume 128. Each ofthe regenerator modules of the device 300 are described above and may beconfigured with the same variations that are also described above inrelation with each respective regenerator module.

As further shown in FIG. 5, the fluid control unit 304 includes internalflow passages leading from the second regenerator module R₁ to a fluidport 310 and the internal flow passages are lined with a layer ofthermally insulating material such as the thermally insulating tubesdescribed above. The flow passages include a short longitudinal passage308 interconnecting with the second regenerator module R₁ and a radialpassage 312 extending to the fluid port 310.

Generally, the refrigeration device 300 utilizes three distinct andseparated regenerator matrices disposed between the expansion space 142and the gas compression volume 128 for exchanging thermal energy withthe working refrigeration fluid of the device. Each of the regeneratormatrices 164, 182 and 216 has a regenerator effectiveness that is lessthan 100% regenerator effectiveness but the three regenerator matricesused in combination provide a regenerator effectiveness of 100%.Accordingly, the thermal regenerators of the device 300 are configuredto receive refrigeration gas from the expansion space 142, at a coldtemperature of approximately 77.degree. K, and to sufficiently warm therefrigeration gas as it flows through the first regenerator matrix 164and then through the second regenerator matrix 182 and then through thethird regenerator matrix 216, to deliver the refrigeration gas out ofthe third regenerator matrix 216 at a warm temperature of approximately270.degree. K. Of course other refrigeration device configuration mayoperate at other cold and warm temperatures without deviating from thepresent invention.

The refrigeration device 300 may be configured with a first regenerator164 having an even shortened longitudinal length L for furtherminiaturizing the refrigeration device 300 or its gas expansion unit112. In particular, with the second regenerator matrix 182 configuredwith a second regenerator effectiveness equal to the regeneratoreffectiveness of a length .DELTA.L of the first regenerator matrix 164and with the third regenerator matrix 216 configured with a thirdregenerator effectiveness equal to a length ΔL of the first regeneratormatrix 164, the first regenerator matrix 164 can be shortened by alength ΔL+ΦL, while still providing 100% thermal regeneratoreffectiveness in the refrigeration device 300.

Referring now to FIG. 7, an external view of the preferred embodiment ofa refrigeration device 100, according to the present invention, is shownin isometric view. In particular, a unitary crankcase 118 integrallysupports the gas compression unit 110 and the volume expansion unit 112.In the view shown, the refrigeration device 100 is configured to cool aninfrared sensor, not shown. The infrared sensor is attached to the coldend of the volume expansion unit 112 and surrounded by a dewer 320. Thedewer 320 provides a vacuum chamber surrounding the infrared sensor tothermally insulate the sensor from surrounding air. A pluralityelectrical connecting pins 322 interconnect with the infrared sensor andcarry sensor signals out of the dewer 320.

The unitary crankcase 118 also integrally supports a rotary DC motor324. The motor 324 includes a rotating shaft, not shown, and a drivecoupling, not shown. The drive coupling converts shaft rotation intolinear motion and drives each of the compressor drive link 130 and thevolume expander drive link 144 in a desired phase relationship forgenerating refrigeration cooling. In the embodiment of the device 100shown in FIG. 7, the fluid conduit 114 is formed integrally with thecrankcase 118.

It will also be recognized by those skilled in the art that, while theinvention has been described above in terms of preferred embodiments, itis not limited thereto. Various features and aspects of the abovedescribed invention may be used individually or jointly. Further,although the invention has been described in the context of itsimplementation in a particular environment, and for particularapplications, e.g. as a Stirling cycle refrigeration device, thoseskilled in the art will recognize that its usefulness is not limitedthereto and that the present invention can be beneficially utilized inany number of environments and implementations including but not limitedto thermal regenerator combinations used in other heating and coolingdevices. Accordingly, the claims set forth below should be construed inview of the full breadth and spirit of the invention as disclosedherein.

What is claimed is:
 1. A method comprising: flowing a refrigeration gasthrough a first regenerator matrix disposed entirely within aregenerator tube, wherein the regenerator tube is located in a coldfinger tube and forms part of a gas displacing piston; and flowing therefrigeration gas through at least a second regenerator matrix, whereinthe at least second regenerator matrix is physically separated from thefirst regenerator matrix by a thermal barrier and a first fluid passageextending from the first regenerator matrix.
 2. The method of claim 1,wherein the first regenerator matrix and the at least second regeneratormatrix are configured to provide approximately 100% thermal regeneratoreffectiveness with respect to the refrigeration gas flowing through thefirst regenerator matrix and the at least second regenerator matrix. 3.A refrigeration device configured to perform the method of claim 1,wherein the refrigeration device comprises an infrared sensor thermallycoupled to and cooled by a distal end of the cold finger tube.